A typical phased array radar system includes a number of transmit and receive modules each driven at a certain amplitude and phase. A beam steering generator sets the amplitude and phase of each transmit module. In this way, the radiation pattern is reinforced in a certain direction and suppressed in undesired directions.
The cost of such a system is typically driven by sensitivity which is a function of the number and design of the active transmit and receive modules. Phased array radars provide a spatial degree of freedom to shape the transmitted beams. Fully focused beams can be generated for high sensitivity missions and shaped and spoiled beams can be generated for lower sensitivity missions. The well-known Cosecant-squared beam pattern provides many of the advantages of sensitivity time control to avoid saturation and short pulse operation to minimize clutter return from uncompressed pulses.
An idealized phased array radar with a Cosecant-squared antenna pattern exhibits an optimal signal-to-noise ratio with low side lobes close to the radar site to detect targets in the presence of ground clutter.
Actual phased array radar systems, however, often have failures of the individual transmit and receive modules and/or include transmit and receive modules which are not used to produce the main beam. Other array blockages and voids are created by the presence of auxiliary and dummy elements.
As a result, the transmitted Cosecant-squared antenna pattern may have high side lobes which degrade effective clutter rejection.